In a power generation system, a combustor is provided at an upstream side of a turbine, and a high-temperature working fluid flows from the combustor to the turbine. In the turbine, a turbine rotor is accommodated in a turbine casing, and the turbine rotor rotates by the supplied working fluid. At the power generation system, power generation is performed by a power generator driven by the rotation of the turbine rotor.
In the power generation system, an operation of the turbine is performed by using a high-temperature and high-pressure working fluid so as to improve a power generation efficiency. For example, when a gas turbine is used in the power generation system, there is a case when combustion gas at 1700° C. is used as the working fluid. Besides, it is proposed that carbon dioxide (CO2) whose temperature at an entrance of the turbine is 800° C. or more and pressure is 20 MPa or more is used as the working fluid.
When the high-temperature and high-pressure working fluid as stated above is used, there is a case when a mechanical strength of the turbine casing is lowered resulting from the operation over a long term. Accordingly, it is proposed to cool a part and so on where the working fluid is introduced in the turbine casing by using a cooling fluid so as to improve reliability of the turbine casing.
However, there is a case when it is not easy to enable high reliability because the turbine casing is not able to be enough cooled.
Besides, it is conceivable to form the turbine casing with a material such as an Ni-based alloy to increase safety of the turbine operated by the high-temperature and high-pressure working fluid. However, the material such as the Ni-based alloy is expensive, and a manufacturing cost increases. Besides, when a large-sized structure such as the turbine casing is manufactured by the Ni-based alloy, there is a case when a lot of defects such as a shrinkage cavity occur. There is a case when it is difficult to improve the reliability resulting from circumstances as stated above.
Accordingly, a problem to be solved by the present invention is to provide a turbine and a power generation system capable of enabling high reliability.